(1) Field of the Invention
The present invention relates to an apparatus for storing data therein and particularly relates to a data storing apparatus for storing various kinds of data and for protectively holding the various kinds of data while a vehicle is running during an unsteady (emergency) state without loss of data.
(2) Background of the Art
In recent years, data storing apparatus for storing various data while a vehicle is running has been installed in the vehicle in order to analyze data stored in the data storage device so that a cause of unsteady operation of the vehicle is determined.
Various types of data storing apparatus have been proposed and developed as exemplified by a Japanese Publication, an automotive engineering volume 40, No. 10, pages 1337 to 1342 (in 1986), and SAE (Society of Automotive Engineers) PAPER 840437 (in 1984).
One of the various types of data storing apparatus disclosed in the above-identified publications is described below.
Various kinds of data relating to running of the vehicle are stored on the basis of a control command by means of an 8-bit microcomputer. The microcomputer is connected to a plurality of interface circuits and a plurality of timer modules via a system interface circuits and a plurality of timer modules via a system bus. The microcomputer processes a variety of information obtained via the interface circuits and/or timer modules.
A first interface circuit transmits switching information from a key switch to a system bus. A second interface circuit transmits a status signal to the system bus. Furthermore, a timer module transmits the measured information from a fuel gage to the system bus. Another timer module transmits speed information from a vehicle speed sensor to the system bus.
A RAM (Random Access Memory) in a working area of the apparatus processes the information obtained via the system bus on the basis of control commands derived from the microcomputer. A RAM data area sequentially stores a variety of data processed by the RAM on the basis of other commands of the microcomputer. In addition, the microcomputer diagnoses causes of unsteady operations of the vehicle on the basis of various types of data stored in the RAM. The results of diagnoses are transmitted to a display unit via a third interface circuit and a display driver to display the results of diagnoses through the display unit.
In the above-described data storing apparatus, in a case where the unsteady operation should occur and/or an accident or trouble should occur, a secondary battery is used to back up the second RAM. Alternatively, an Erasable Programmable Read Only Memory (EPROM), Electrically Erasable Programmable Read Only Memory (EEPROM), or Non-Volatile Random Access Memory (NVRAM) is used as storage means for storing the various data in order to ensure and protect the stored data.
The EEPROM includes address buffers, as well as row and column decoders. The address buffers respond to an addressing word derived (i.e., an address of data to be written is specified) from the microcomputer. The row and column decoders specify a particular memory cell of the memory array. Writing or reading of data is executed in response to a high voltage signal derived from a control circuit for the specified memory cell.
However, since the EEPROM stores data composed of a plurality of bits, a long time is required to execute data write and read questions if a large amount of data is handled. Therefore, the protection of data during unsteady vehicle operation often becomes difficult.
A NVRAM (Non-volatile Random Access Memory) has, in turn, been used in which the RAM and EEPROM are integrated onto a single chip.
The NVRAM usually functions as a RAM and can read or write the data at high speeds from a Random Access portion thereof. In addition, an NV (non-volatile) signal commands, as necessary, writing of data supplied to one input terminal of a logical product circuit in the case of unsteady (or emergency) operation so that data are written at high speeds from the random access portion to the non-volatile portion.
Although the NVRAM can shorten the time required to write data in case of emergency, one of the addresses must be specified when the data are stored in the random access memory portion. Therefore, processing required to store the data becomes complicated.
Although it is possible to use a custom NVRAM in which each address is automatically generated during writing of data into the specified address, a circuit constructed at the periphery of the custom NVRAM becomes complicated, resulting in increased cost.
On the other hand, an LSI (Large Integrated Circuit) composed of a plurality of so-called CMOS (Composite Metal Oxide Semiconductor) transistor circuits as memory cells can form the second RAM to store the data indicating parameter for the running vehicle.
Since there is a limit for the quantity of data to be stored per chip, an improvement is needed for the storing means for storing the large quantity of various data related to running of the vehicle.